The Role of the Integrated Stress Response in the Biologic Response of Keratinocytes to UVB Exposure

Abstract

Background and Hypothesis:Ultraviolet B (UVB) irradiation from the sun can disrupt normal epidermal keratinocyte function, leading to the development of skin cancer. The integrated stress response (ISR) is a conserved cellular mechanism against environmental stressors, such as UV irradiation, through the phosphorylation of the alpha subunit of the initiation factor eIF2 (eIF2a-P). Previously, we demonstrated that the ISR kinase GCN2 plays a role in the response of keratinocytes exposed to UV irradiation. However, the role of other components of the ISR in UV-induced stress has not been well elucidated. We hypothesize that in addition to GCN2, other components of ISR such as PERK, GCN1, and ZAK1 are involved in apoptotic pathways induced by prolonged UVB exposure. Methods:Gene-specific knockouts (KO) were generated using CRISPR/Cas9 and validated through immunoblotting. Wild-type (WT) and KO NTERT keratinocytes were irradiated with UVB at 0, 100, 200, and 400J/m2. Six hours post-UVB, cell photomicrographs were taken at 0 and 400J/m2. Measurements for apoptosis were then performed by measuring enzymatic levels of caspase-3. Results:Measurements of caspase-3 following UVB exposure on WT NTERT, PERK-KO, and GCN2-KO showed no difference between the groups. GCN1-KO had significantly greater caspase-3 activity at 400J/m2, whereas ZAK1-KO had significantly reduced caspase-3 activity at the same concentration. GCN2/PERK double-KO had significantly increased caspase-3 activity at 400 J/m2 compared to the individual KO cells. Conclusion and Potential Impact:Collectively, our data suggests that the ISR may be involved in the apoptotic responses that ensue in keratinocytes exposed to UVB. How GCN2 and PERK could co-interact with GCN1 or ZAK1 to facilitate apoptotic fate in keratinocytes still warrants further research. Nevertheless, elucidating the role of the ISR in normal keratinocyte response to UV irradiation will allow us to define novel therapeutic targets for the treatment or prevention of UV-related skin malignancies.